Concentrated photographic fixing



United States Patent CONCENTRATED. PHQTOGRAPHIG FIXING SOLUTIONS RichardW. Henri, Rochester, N. .assignor to Eastman Kodak Company, Rochester,N. Y., a corporation of New Jersey No Drawing. Application Jul 26, 1954,Serial No. 445,933

Claims. (or. 95am) This invention relates to photographic fixing agentsand more particularly to concentrated photographic fixing solutions andmethods for their preparation.

Heretofore concentrated fixing solutions have been prepared whichemployed only those ingredients which would conveniently dissolve, orallowed sorne excess of crystals to accumulate in thesolution. Theseexcess crystals required vigorous application of shaking and stirring tor'esuspend before dilution and, due to coarseness, are slow to dissolve.

An object of the present invention is therefore to provide novel methodsof obtaining highly concentrated fixing solutions. Another object is toprovide methods of preparing stable, readily soluble suspensions of theingredients of photographic fixing baths. Another object is to providefixing solution concentrates which provide rapid solution and obviatedusting. Other objects will appear hereinafter.

In accordance with one feature of the present invention these objectsare by suspending finely ground or finely divided crystalline elementsof the fixing solution in a highly soluble colloid. Colloidsparticularly suitable for this purpose are esters of alginic acid. Theseare available commercially under the trade names Kelcoloid LV, KelcoloidLVF, Kelcoloid HV, and Kelcoloid HVF.

In accordance with another feature of this invention, in case of fixingsolutions containing sodium thiosulfate, no extraneous colloid need beadded, the stability being apparently achieved through the hydratingaction of the anhydrous form of sodium thiosulfate.

It is proposed as a mechanism, the correctness of which, of course, inno way limits my invention, that the stable suspension is formed in thefirst instance through a weak gelation or cross-linking of the polymericalginic acid ester, and the concentration of the solid ingredients hasnot been found to be critical. In the second instance, it is presumedthat the formation of a stable suspension occurs through the hydratingaction of the sodium thiosulfate which takes up most of the excesswater, but this hydrating action is not sufficient to remove entirelyall fluidity. In this instance the proportion of water included is morecritical than when the algin colloid is employed.

It is considered desirable, when preparing these gels, to obtain astifily fiuid state, rather than a complete rigidity. Suitable particlesize for the suspended solid particles lies between 40 mesh and 100mesh, although there would be no objection to finer particles. Theoptimum concentration of the colloid protectant will vary with itsmolecular weight (viscosity) and with the composition of the fixingbath. In the case of the low viscosity form of the propylene glycolester of polymeric alginic acid (marketed under the trade name ofKelcoloid LV), a concentration of 2 to 4 per cent is appropriate, iflittle assistance is obtained from the hydrating action of theingredients. A concentration of chemical ingredients in the order of 1gram per cc. is common.

i vaiitageous in some instances, particularly where the 2- Theincorporation of an antifoaming material 'is adcolloidal algin isemployed, and a silicone preparation;

Dow-Corning .D. C. Antifoam Emulsion has been found suitable.

The invention is further illustrated in the following examples:

Example 1.--S0dium thiosulfate fixer A mixture containing:

Grams Sodium thiosu'lfa'te, anhydrousm 70.0 Potassium aluminum sulfatel2H2O 12:0 Boric acid- 1 1 7.4 Sodium bis lfite s z i 6.0 Sodium acetate7.2

was added to 60' cc. of a 0.1% solution of Kelcoloid LV; The mixture wasfinely ground and produced a stifiiy fluid solution of about cc. volume.It dissolved rapidly and without diificulty to produce a solution ofnormal fixing properties.

Example 2.-S0dii4m-ammonium thiosulfate fixer The following hardenerconstituents Grams Sodium acetate 30.0 Potassium aluminum sulfate l2HzO30.0 Boric acid 15.0 Sodium bisulfite 10.0 Sodium citrate 3.0

Example 3.Ammonium thiosulfate fixer To cc. of 76% ammonium thiosulfatesolution were added 5.2 grams of Kelcoloid LV, which was allowed tostand for 4 days, until dissolved. Then 4 drops of DC Antifoam Emulsionwere added and 60 grams of a hard ener, prepared in the proportions ofExample 2. This produced a stable fixer of about cc. volume whichdissolved readily and without foam difficulty. A higher thiosulfate ionconcentration was achieved, however, without essentially increasingvolume, by the further addition of 50 grams of anhydrous sodiumthiosulfate. This alternative mixture was also readily soluble andstable, and produced an active fixer when diluted 1 part to 7 parts ofwater.

Example 4.S0dium-amm0nium thiosulfate fixer To a mixture of thefollowing hardener ingredients Grams Sodium acetate 15.0 Boric acid 7.5Sodium citrate 1.5 Ammonium aluminum sulfate 5.0 Sodium bisulfite 5.0

60 cc. of a 76% solution of ammonium thiosulfate was added slowly, withgrinding and stirring. Then 80 grams of anhydrous sodium thiosulfatewere added, and grinding continued. Finally, an additional 5 cc. of theammonium thiosulfate solution were added. This formed a stiffly fluidmixture, which dissolved readily on dilution with water and provedstable in prolonged incubation tests.

Example 5 The following ingredients were ground together in a mortar:

Sodium acetate grams 15.0 Boric acid do 7.5 Sodium citrate do 1.5Ammonium alum do 5.0 Sodium bisulfite do 5.0 Ammonium thiosulfate, 76%solution, weight volume cc 65.0 Sodium thiosulfate, anhydrous grams 75.0

This gel was found to be entirely stable in accelerated aging testsincluding incubation at 110 F. for a period in excess of four months.Added to ten parts of water, it produced a clear solution which activelyfixed both negative and positive films.

I have found that the concentrate made in accordance with this inventionis quite efiective and provides faster solution and obviates dusting.

I claim:

1. A photographic fixing composition in suspension in a colloidal gel,comprising a water soluble colloidal gel of an ester of alginic acid andsuspended therein a thiosulfate selected from an alkali sulfite and anammonium sulfite, a hardening agent, boric acid and a salt of a solid 4organic acid selected from the group consisting of acetic acid andcitric acid.

2. A photographic fixing composition in suspension in a colloidal gelcomprising a water soluble colloidal gel of an ester of alginic acid andsuspended therein sodium thiosulfate, potassium aluminum sulfate, boricacid, sodium bisulfite and sodium acetate.

3. A photographic fixing composition in suspension in a colloidal gelcomprising a water soluble colloidal gel consisting of propylene glycolalginate and suspended therein sodium thiosulfate, potassium aluminumsulfate, boric acid, sodium bisulfite and sodium acetate.

4. A photographic fixing composition in suspension in a colloidal gelcomprising propylene glycol alginate gel, sodium acetate, boric acid,sodium citrate, ammonium alum, sodium bisulfite, ammonium thiosulfate,and sodium thiosulfate.

5. A photographic fixing composition in suspension in a colloidal gelcomprising propylene glycol alginate gel, sodium acetate, boric acid,sodium citrate, ammonium alum, sodium bisulfite and sodium thiosulfate.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PHOTOGRAPHIC FIXING COMPOSITION IN SUSPENSION IN A COLLOIDAL GEL,COMPRISING A WATER SOLUBLE COLLOIDAL GEL OF AN ESTER OF ALGINIC ACID ANDSUSPENDED THEREIN A THIOSULFATE SELECTED FROM AN ALKALI SULFITE AND ANAMMONIUM SULFITE, A HARDENING AGENT, BORIC ACID AND A SALT OF A SOLIDORGANIC ACID SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID ANDCITRIC ACID.